主题：从字符串“”到类型“Double”的转换无效。

    For Each drs As DataRow In DataTables("统筹分配_统筹分配").Select("")
        cnt = drs("数量")
        drs("剩余") = drs("数量")
        fors = DataTables("门店等级表").Compute("max(配货数量)", "门店等级='A'")
        For i = 1 To fors
            For Each djbs As DataRow In DataTables("门店等级表").Select("门店等级='A'")
                MessageBox.Show(djbs("配货数量").ToString)
                MessageBox.Show(drs(djbs("仓库")).ToString)
                MessageBox.Show(String.Compare(djbs("配货数量").ToString, drs(djbs("仓库")).ToString, True))
                If djbs IsNot Nothing And cnt > 0 And String.Compare(djbs("配货数量").ToString, drs(djbs("仓库")).ToString, False) Then
                    If Tables("统筹分配_统筹分配").Compute("sum(剩余)", "款号='" & drs("款号") & "' And 花色='" & drs("花色") & "' and 尺码 = '" & drs("尺码") & "'") > "0" Then
                        drs(djbs("仓库")) += 1
                        cnt = cnt - 1
                    End If
                End If
            Next
        Next     
        drs("剩余") = cnt
    Next

字符串要怎么向上加1，以下语句有问题

drs(djbs("仓库")) += 1

从字符串“”到类型“Double”的转换无效。